[PATCH] mm/userfaultfd: compare exact registration modes before skipping

[Gregory Price]

Changing registration from MISSING|WP to WP returns success but leaves
MISSING enabled. The no-op check sees that WP is already set and skips
the update, so later accesses to missing pages still wait for userspace.

Skip the update only when the current and requested UFFD modes match
exactly.

Fixes: 63b2d4174c4a ("userfaultfd: wp: add the writeprotect API to userfaultfd ioctl")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>
[ david: apply fixup from Lorenzo ]
Signed-off-by: David Hildenbrand (Arm) <david@xxxxxxxxxx>
---
 mm/userfaultfd.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 710e913c73bf..24b7a2612469 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -2291,6 +2291,7 @@ static int userfaultfd_register_range(struct userfaultfd_ctx *ctx,
 
 	for_each_vma_range(vmi, vma, end) {
 		const bool any_mode_removed = vma->vm_flags & __VM_UFFD_FLAGS & ~vm_flags;
+		const vma_flags_t curr_vma_flags = vma_flags_and_mask(&vma->flags, __VMA_UFFD_FLAGS);
 
 		cond_resched();
 
@@ -2304,7 +2305,7 @@ static int userfaultfd_register_range(struct userfaultfd_ctx *ctx,
 		 * userfaultfd and with the right tracking mode too.
 		 */
 		if (vma->vm_userfaultfd_ctx.ctx == ctx &&
-		    vma_test_all_mask(vma, vma_flags))
+		    vma_flags_same_pair(&curr_vma_flags, &vma_flags))
 			goto skip;
 
 		/*
-- 
2.43.0


-- 
Cheers,

David